powerpc/perf: Add missing SIER support

Commit 8f61aa32

 "Add support for SIER" missed updates to siar_valid()
and perf_get_data_addr().

In both cases we need to check the SIER instead of mmcra.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>